Salt water concentration with alumina-silica additive and separation of sodium sulfate-calcium sulfate double salt



United States Patent ()fiice 3,358,740 Patented Dec. 19, 1967 s sss 740 SALT WATER CONCENTRATION WITH ALU- MINA-SILICA ADDITIVE AND SEPARATION or SODIUM SULFATE-CALCIUM SULFATE DOUBLE SALT This invention relates to a method for concentrating salt water such as sea water, sea brine, and natural brine. When salt water, for example sea water, is concen example, method for operating in the condition containing 1-3% of CaCO and Mg(OH) in heated salt water, method for preventing the formation of scale in which bicarbonate ion is decomposed by adding FeCl -6H O is converted to Fe(OH) and the method in which mineral acid is added to salt water to be treated and so on. But these methods have the defects that expected effects cannot be obtained or corrosion of the apparatus is increased etc., and can not bring satisfactory result.

As a preliminary step to obtain an improved method of preventing the formation of scale, the inventor has conducted the following two experiments.

Experiment I 7 liters of sea water boiled and evaporated under ditrated by heating, bicarbonate ions in the solution are rect heating and agitation to obtain a concentration of subjected to thermal decomposition, releasing carbon di- 18.8 Be. The materials separated in this process were oxide and at the same time forming calcium carbonate and analysed and the following result was obtained as shown magnesium hydroxide which form scale on the heating in Table I.

TABLE I CaCO Mg(OH)z MgCOa Nazsol-oasol casol Total Grams 0. 2496 0.0226 0. 0530 1. 6260 4.1254 6.0766

Percent 4. 10s 0. 372 0. s72 26. 756 67. 891

surfaces, thereby the heat conductivity is reduced. Fur- All the materials described above adhered to the surface thermore, hydrochloric acid is produced as a result of of the heater and formed scale. the thermal decomposition of magnesium chlorideat the Experiment H surfaces having scale adhered thereto, and corroslon of the a aratus is incr ased by th produced hydrochloric Nltrlc acid to neutralize the alkalinity was added to sea aicd as w ll s b th bo di id water as used in Experiment I and the experiment was There have been various proposals for mitigating the repeated. The result shown in Table II was obtained.

TABLE II C co Mg(OH)a MgCOs NazSO4-5CaSO -3Hn0 CaSO4%HaO Total Grams 0. 0075 0. 0474 0 7.0014 1. 4112 8.5934

Percent 0.087 0-551 0 8 .242 17.120

difficulty but none of them satisfy industrial requirements. In this case, separated materials were wholly in floating It is, therefore, an object of the present invention to state 1n the heating liquld and where not changed to scale. provide a process for concentrating the salt water without Separated matoflals 111 two GXPoTHIIoHPS described above the defects described above and which prevents formaa eas O H 1I 1 bles, but observation of phenomena tion of scale effectively in which salt water is concenduring p a q s also o Interest y, 1n p trated in existence of a kind of or many kinds of the mom all boglhnlng of heating, o p hllbhles Come material selected among silica, alumina or alumino siliout o y h area hllrrouhdlhg the agltatihg hlados cate etc., thereby bicarbonate ion involved in salt water Showing bubbling condition, but when CaCO, beglns to i o t d t non t lli M co ith t i d i adhere to the heating wall following advancement of conf f r ti of scale as lli C c0 F h centratlon, evaporated bubbles move to the adhered surth bj t of thi invention i to remove SO i face and thereafter bubbling took place only on the heatmother liquid as in form of Na SO -CaSO type double mg Suffaoosalts, on extracting and utilizing components contained in These Observed facts and th result shown 1n Table I salt water by concentration, S0 is undesirable at each leach that the S6511? formatloh Comes from following step of procedure and complicates the separation of comp namely adhesion to the hoahhg Surface of Cacos ponents h other d fo m the i cause for lowering produced as a result of decomposition of bicarbonate, and the quality of products, so that various methods for refollowlhg advahhlhg of concentration of C3804 as moving these defects have been attempted heretofore. CaS041/2H20, and 011 further concentration z 4' However in all of them eparation was dimcult and co t 1SI separated. These were heated further and was hi h d especiany i case reagents were added, as followlng reactions occurred resulting in solidifications. solvent, to salt water, such reagents were used as an CaSO4 2H2o CasO4fl1/2H2O+1%H2O aqueous solution, and as a consequence, the additlon of caso 3/2 H 060150 1/ H 0 such solution decreased the efliciency of the operation Na i because the solution served to dilute the liquid which was 2 5 6 3H 8 to be concentrated. In the method of the present inven- 4+ 3 4+ 2 tion, either calcium chloride or, solid CaSO -2H O is Referring to the sea water used in Experiment H, bicaradded directly to produce Na SO -CaSO -3H O, a doubonate ion was decomposed by neutralization and could ble salt. not ex1st in the heated liquid, so that CaCO as the basis As described above, in order to prevent formation of scale, many methods have been proposed already, for

for the induction of separation of solid, could not be obtamed and as a result there was no formation of scale.

From the results of the experiments described above and observations therefor, the inventor studied a suitable neutralizing means under presumption that when the alkalinity in sea water is neutralized same result may be obtained notwithstanding whatever neutralizing means may be adopted, and as a result it Was found that materials such as silica, silicic acid, alumina, alum-inc silicate of kaolin, acid clay, bentonite and zeolite etc., are very suitable neutralizing material for this purpose. This invention is based on this novel finding. When the material is added to sea water and heated for concentration, the greater part of alkali content of sea water disappears and pH is lowered from 8.3 to 7; separation of CaCO is restrained and only MgCO can remain in the liquid and scale does not appear at all. And yet the quantity of the addition is in order of only 0.1% of sea water and moreover even in the state that the scale has appeared already when the material is added, scale can be separated, and this is excellent effect.

EXAMPLE I Using a glass vessel, liters of sea water were evaporated until scale appeared on the heating wall. Then 1 gr. of silicic acid Was added thereto and 2 liters of fresh sea water were added and heating was continued. The scale adhered was removed perfectly. The separated materials were filtered and washed with alcohol and ether and analysed as shown in the following Table III.

(1) N 0 change appears, in the infrared spectrophotometry of the material before and after evaporation;

(2) There is no change in chemical constitution;

(3) Function of the material is endurable for continuous usage;

(4) When silioic acid is heated, solubility shows the value of 200 p.p.m., but it separates silicic acid on heating and concentration;

Further explanation referring to detailed investigation is omitted, as it is not intended that the scope of the invention should be limited by any theoretical explanation.

By the way, in this heating concentration, when CaCl is added, in the presence of the material in step of concentration, CaSQ is separated in the first place but in progress of concentration a double salt of Na SO -CaSO type appears in the form of a suspension in the heating liquid. Accordingly, it is appreciated that all S0,;- becomes CaSO and scale formation is prevented.

In this case, it is also assured that double salt of CaSO and Na SO -CaSO type may be separated respectively in the form such as C850 2H O, CaSO /2H O, 2Na SO CaSO; 2H O Na SO -5CaSO -3H O and Na SO.,,-CaSO1 etc., accordiing to temperature and concentration of the heating liquid.

' Ordinarily, Na+ in salt water is considered to be separated as NaCl by heating concentration, but in this in- TAB LE III Specific Bauln OaCOs MgCO; NazSO4-5CaSO4-3H2O CaSO H 0 Total gravity 1.14708 18.5 Grams 0.1243 0. 6813 7. 0005 0. 0526 7.858

' 1. ass 8.660 89.079 0. 669 100.00

In this example, the reason that the amount of CaCO contained showed a rather larger value than that of Example 11, may be that the parts contained in the inner part of the scale could not be brought into direct contact with solution.

EXAMPLE II The evaporating tests as in Example I were made by application of various kinds of the material at the beginning of heating and the results obtain d, are shown in Table IV. In all six examples employing silicic acid, alumina, bentonite, etc., scale did not appear and all separated materials floated in the liquid and white muddy suspension was obtained.

vention it can be separated in a form of double salt as Na SO 'CaSO so that the process may be varied if necessary, and the process can be adopted freely in broad extent such as manufacture of electrolyte by diaphragm process, or manufacture of magnesium hydroxide from sea brine and bittern, or extraction of Na+ in salt water as Na SO In converting S0 ions contained in salt water to a boduble salt, the following several methods may be considered. In case the addition of Ca++ for example, CaCl is adopted, the amount of the latter is determined on the SO; content in the salt water. In case (12180., is suspended in the salt water, or in case CaSOyZI-I O in the suspended state is added to the sea water, the upper TABLE Iv Separated mother Material separated l qu Additionmaterial (quantity) U as n .1

Specific Benn-1e CaGOs MgCOs, Na1SO -5CaSO4-3H 0 CeSm-V EhO Total 7 av ty Grams 0. 005.7 0. 4740 5.9761 0.5870 7.0428 5111010 nd u s-l 1.). 1.1305 .0 {Percent 081 6,750 8,855

, Grams- 0. 0524 1. 3125 4. 0250 0. 4517 s. 8779 Alumina 2 1 0 13609 ilereent, 1. 0823 22. 13 68. 470 7.788 rams 0.03s 0. 5.8190 1. 7203 8.3'22 Bentu aw 0 1 M 114438 {Percent 0. 161 0.4s0 60.407 20.656, Grams- 0.1162 0. 0140 3.7145 0.0626 4.5682 An y 11-1 1332 {P'91'0611l2 2. 543 1 3 459 821622 13. 712 Grams..- 0 .433 .09, 0 0.9176 3.4473 Kaolm e-/ {PercenL 0 9 12. 31 60. 802 26. 617

. 1 G 11.. 0.021 0. 1 0. 5150 0.132 1 ."0 Slhea plus Acid clay (0.5 g.+0.5 s-1. 1.1110 16.1 jf m 15367 107 16 754:7 0 1 10 EXAMPLE III limit of the amount to be added is determined depending Evaporation tests were made in the same, Way as in Examples I and 11 except that an iron vessel was used in place of glass. The results were the same as obtained in Examples 1" and Hand no corrosion of the iron vessel was seen.

on the Na+ content in the salt water. CaSO which is added to the heated salt water reacts in the following manner, namely:

and accumulation of CaCl increases gradually and accordingly SO in salt water reacts as follows:

which is separated at the beginning serves as seed crystals and is formed in large crystals. Since which has separated is present in the form of suspension in the heated liquid, it can be discharged from the heating-still together with the concentrated liquid corresponding, in amount, to the added salt water if an overflow pipe is provided in the heating-concentrating vessel. Since the discharged double salt is produced in large crystals, it precipitates rapidly if left undisturbed and thus it can be separated easily from the concentrated liquid. By subjecting the separated salt to hydrolysis, Na SO becomes dissolved and CaSO -2H O can be separated as crystals. Na SO solution obtained can be used as raw material of anhydrous G-laubers salt, while CaSO -2H O is used repeatedly for producing double salt. As described above, Na+ contained in salt liquid can be obtained as Na SO from salt liquid and at the same time desulfurization can be carried out.

The temperature for producing Na SO -CaSO -3H O is 93 C., but when CaSO -2I-I O is added directly to salt water double salt is produced and separated instantaneously and no time is given for crystal growth so that fine crystals with high surface area per unit weight are obtained, resulting in an increased amount of the adhering mother liquid. The Na SO solution obtainable by bydrolysis then becomes impure, and therefore, attention must be paid so as to obtain as large crystals as possible, While giving ample time for the growth of Crystals to obtain minimum surface area per unit weight. This is illustrated in the following experiments.

Experiment III g. of CaSO -2H O is added to 200 ml. of sea brine at 189 B. and heated, then at 93 C., fluidity of liquid is lost and the mass becomes pasty. Next separating the crystal, the composition was found to be 98.67% of Na SO -5CaSO -3H O and 1.33% CaSO /zH O.

Experiment IV While sea brine at 18.9" B. is heated, sea Water (1.365 g./l. of CaCl added) corresponding to the amount of vaporized part thereof is added, then 4.2 g./l. of double salt can be obtained.

Experiment V While sea brine at 189 B. is heated, sea water (suspended at the rate of CaSO -2H O 2 g./l.) corresponding to the amount of vaporized part thereof is added, and 10.1 g./l. of double salt was obtained.

The result obtained by analyzing the amount of mother liquid adhered (cc./ g.) shaked ofi from the double salt obtained by said experiments using centrifugal separating machine showed the following value:

, Cc. Experiment III 0.551 Experiment IV 0.096 Experiment V 0.122

every one is costly and separation is diflicult especially when agents are added because the concentrated liquid becomes diluted because such agents are used in the form of solution and as a natural result the efilciency of operation is lowered. According to the method of this invention, solid CaSO -2H O is added directly to salt Water and can be recovered as Na SO -CaSO -3H O, and thus removable of sulfate from the raw material can be maintained, so that it is very advantageous.

EXAMPLE IV 10 g. of CaSO -2H O is added to 200 ml. of sea brine at 203 B. Then 1.0 gr. of silicic acid was added thereto and after heating the mixture liquid, a part of the mixture was taken as the mother liquid I, and further CaSO -2H O was added to the remaining mother liquid I, and was heated. A part of the latter liquid was taken as the liquid II. These sample liquids I and II were analysed with respect to the composition and the degree of the residual 80.; ions. The results are shown in the following Table V.

What I claim is:

1. In a method for concentrating salt Water, the improvement comprising evaporating water from said salt water in the presence of at least one additive selected from the group consisting of silica, silicic acid, alumina, an aluminosilicate, acid clay, kaolin, and bentonite to reduce scale formation.

2. A method according to claim 1, wherein said additive is silicic acid.

3. A method for concentrating salt water and for converting sulfate ions in the salt water to a double salt, comprising the steps of evaporating water from said salt water in the presence of (a) at least one additive selected from the group consisting of silicia, silicic acid, alumina, an aluminosilicate, acid clay, kaolin, and bentonite and (b) a calcium compound selected from the group consisting of calcium chloride and calcium sulfate, whereby scale formation is reduced and sulfate ions originally present in the salt water are converted to a sodium sulfate-calcium sulfate double salt.

4. A method according to claim 3, wherein said calcium compound is calcium sulfate, and said calcium sulfate forms a suspension in the saltwater.

5. A method according to claim 3, further comprising separating the produced double salt, and subjecting the double salt to hydrolysis to separate the double salt into sodium sulfate and calcium sulfate dihydrate.

6. A process according to claim 5, wherein the calcium sulfate dihydrate is recycled for use in forming additional double salt.

7. A method according to claim 3, wherein the temperature during evaporation is approximately 93 C.

References Cited UNITED STATES PATENTS 2,403,174 7/1946 Ernst.

2,733,196 1/1956 Hillier 2037 2,979,442 4/ 1961 Badger 2037 3,000,795 9/1961 Goeldner 2037 X 3,119,752 l/ 1964 Checkovich 203-34 3,218,241 11/ 1965 Checkovich 20334 3,248,181 4/ 1966 Akimoto 23-304 X 3,262,865 7/1966 Waters 207-7 NORMAN YUDKOFF, Primary Examiner. 

1. IN A METHOD FOR CONCENTRATING SALT WATER, THE IMPROVEMENT COMPRISING EVAPORATING WATER FROM SAID SALT WATER IN THE PRESENCE OF AT LEAST ONE ADDITIVE SELECTED FROM THE GROUP CONSISTING OF SILICA, SILICIC ACID, ALUMINA, AN ALUMINOSILICATE, ACID CLAY, KAOLIN, AND BENTONITE TO REDUCE SCALE FORMATION. 